The present invention relates to processes for treating substrate surfaces, and particularly to a process for removing part of a coating from a substrate using laser irradiation.
In the manufacture of coated substrates such as layered photoreceptors, it is often desirable to uniformly reduce the thickness of a coating in a predetermined region. For example, in producing coated photoreceptors, it is frequently necessary to reduce the thickness of the photoreceptor's seams, taper or seal edges of the photoreceptor, or remove excess material in the "sag" area of a dip-coated photoreceptor drum. Sag areas are regions of thicker coating formed when wet coating material migrates down the side of a dip-coated drum as the drum is lifted out of a coating bath.
Conventionally, coated substrate surfaces are treated to remove excess coating material by applying chemical solvents or by mechanically machining the substrate surface. However, chemical or mechanical treatments often do not provide the treated substrate with a sufficiently uniform and smoothly polished surface suitable for certain commercial uses such as the manufacture of photoreceptors. Chemical treatments can cause solvent droplets or vapor to contact the coating in regions that are not intended to be removed, reducing the quality of the photoreceptor. Furthermore, organic solvents have a limited useful life and are hazardous to work with. Mechanical machining techniques for removing coatings are cumbersome, inefficient, and often produce photoreceptors of unacceptable quality. Moreover, chemical or mechanical treatments do not achieve precise tolerances, which renders such processes unsuitable for reducing the thickness of a coating such as a polymer coating on a predetermined surface region of the substrate.
Japanese Publication No. 3-144,458 discloses an attempt to eliminate mechanical and chemical treatments of coated photoreceptors. A laser beam from an yttrium-aluminum-garnet laser is irradiated at the end portions of a photoreceptor drum to burn or sublimate the photoreceptor coating. Japanese Publication No. 3-194,131 discloses a similar process in which laser energy is directed at the ends of a photoreceptor in an effort to completely remove the coating.
Although these laser treatment processes are intended to completely remove a photoreceptor coating, it has been found that many materials commonly used in photoreceptor coatings are melted, rather than vaporized, by these processes. The molten coating subsequently hardens and must be removed by chemical or mechanical means. Moreover, in some instances it is desirable to uniformly remove only part of the coating, rather than completely vaporize and/or melt the entire coating.